Purification of Substances by Electrodialysis ALBERTL. ELDER,RUSSELLP. EASTON, HAROLD E. PLETCHER, Syracuse University, AND FLOYD C. PETERSON, New York State College of Forestry, Syracuse, N. Y.
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Samples of commercial grape juice were diluted 1 to 1 and placed in the electrodialysis cell. The average of several determinations gave 18 to 20 per cent removal of the tartrate radical present in the grape juice in 3 hours. The flavor of the grape juice was unchanged by electrodialysis. The main pigments, anthocyanins or enins (1, a), in grape juice did not come through the membranes during the electrodialysis.
ANY references are to be found on the subject of
electrodialysis, and new applications and uses are numerous. Most of the data reported in the present paper have resulted from research necessary to obtain a substance of a certain purity for use in some other investigation. The apparatus used in the electrodialysis experiments was essentially that described by Holmes and Elder (4). I n all experiments a piece of platinum foil was placed between the carbon anode and the filter paper. Parchment and Cellophane membranes were used throughout the investigation.
ELECTRODIALYSIS OP SUGARS One difficulty encountered by workers in sugar chemistry is that of preparing the sugar in an ash-free condition. The isolation and purification of arabogalactan by the leadtannate method of Schorger and Smith (5)result in a product which even under very careful purification contains an appreciable amount of ash, only a portion of which under normal conditions is removable by repeated solution and precipitation. This procedure results in a great loss of the purified sugar. The ash content of material purified by such methods is never so low that the sugar may be considered ash-free. Englis and others (3) found that electrodialysis of samples of artichoke sirup, from which levulose is obtained, produced part of the necessary acidification which resulted in a final lower ash content of the levulose. They found that the colloid content of the extract was also reduced. Table I shows typical results in further purification of sugars by electrodialysis. The amorphous powder, sample 111, before electrodialysis was straw-colored and had an ash content of 1.39 per cent. After electrodialysis and subsequent precipitation the sugar was snow-white and contained 0.063 per cent of ash. Aqueous solutions before electrodialysis were slightly turbid, while the dialyzed solutions were perfectly clear, making possible accurate polariscopic readings. The reducing value of the sugar was unchanged by electrodialysis, indicating that no hydrolysis took place during the purification. The maximum temperature during the electrodialysis n7as 55" C.
ELECTRODIALYSIS OF CASEIN Samples of both acid and rennin casein were obtained from the research laboratory of the Borden Company. The ash content of acid casein before electrodialysis was 3.69 per cent and after 56 hours of electrodialysis was 0.067 per cent, a 98.4 per cent removal of ash. The acid casein (8.41 grams) was suspended in dilute acetic acid and diluted to 850 cc. Ammeter readings varied from 0.22 ampere at the start to 0.027 ampere at the end. The maximum and minimum temperatures within the cell were 45" and 25" C., respectively. A sliding resistance was used to keep the cell from heating too much. During electrodialysis a horny material deposited on the cathode membrane, and, when dried, had an ash content of 0.069 per cent. In two other electrodialysis experiments no acetic acid was added, but the acid casein was kept in suspension by vigorous mechanical stirring. Ash removals of 95.2 and 97.3 per cent were obtained after 42.2 and 28 hours, respectively. I n the first of these two runs the ammeter readings were 0.130 maximum and 0.0091 minimum, and in the second 0.425 and 0.0108. Temperature variations were from 26' to 51" C. Of the 11.35-gram sample of acid casein used in the second run, 8.81 grams were recovered by filtering the electrodialyzed solution. Removal of the ash from rennin casein was not as satisfactory. The original ash content was 7.98 per cent and the final 2.17 per cent, an average ash removal of 72.9 per cent. Considerable difficulty was encountered with casein sticking to the mechanical stirrer.
OF SUGARB BY ELECTRODIALYSIS TABLE I. PURIFICATION
Sugar
ELECTRODIALYSIS OF GRAPEJUICE
SAMPLE I Galactose
S A M P LI1~ SAMPLP111 AraboArabogalactan galactan 120 120
Volts 120 Maximum and minimum ammeter readings 0 .012&0.004 0.05-0.0129 0.2-0.006 55'C. 46' C. 26'C. Maximum temperature 72 48 43 Period of electrodialysis (hours) 10 7.6 10.31 Weight of sugar a t start (grams) 7.64 5.02 9.0 Weight of sugar recovered (grama) 1.39 0.156 0.278 Ash content a t start (Der cent) Ash content purified-product (per cent) 0.0135 9&!27 0.063 Ash removal (per cent) 91.3 95.6 Specific rotation Unchanged Not taken Unchanged
It appeared likely that the ash content of unfermented grape juice could be lowered by electrodialyzing out the tartrates present. Cellophane membranes were mounted wet on the cell and held in place by rubber bands. The potential current was held at 120 volts. The drip water was collected through funnels supported below the filter papers which were between the carbon blocks and the Cellophane membranes. I n preliminary experiments Kahlbaum's c. P. potassium acid tartrate was added to water and electrodialyzed, using Sutton's method (6) to determine the tartaric acid in the positive drip, Ninety-six per cent of the potassium acid tartrate was recovered in the drip waters and in the cell; 40 per cent of the 4.08-gram sample placed in the electrodialysis cell was removed in 12 hours by electrodialysis. As a further check on the acid collected in the positive drip, carbon and hydrogen analyses were made, and the excellent checks obtained indicated that nearly pure tartaric acid was obtained in the positive drip water.
The material of sample I11 was prepared from Western American larch wood by the original method of Schorger and Smith ( 5 ) , whereas that in sample I1 was isolated by the method of Wise and Peterson (79, which accounts for the difference in ash content. Reprecipitation of the sugar from samples I1 and I11 by the use of 95 per cent ethyl alcohol gave a product which settled very rapidly and left a clear supernatant mother liquor. The galactose, sample I, was a product of the Pfanstiehl Products Company. Further studies are being made on other simple sugars, polysaccharides, and hemicelluloses. 65
ANALYTICAL EDITION
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LITERATURE CITED
Vol. 6, No. 1
(6) Sutton, “Volumetric Analysis,” 11th ed., p. 123-7, Blakiston,
(3j Dykins, Kleiderer, H k b a u m , Hardy, and Englis, IND. ENG. CHEM.,25, 937 (1933). (4) Holmes and Elder, J. Phys. Chem., 35, 1361 (1931). (5) Schorger and Smith, J. IND. EXG.CHEM.,8, 494 (1916).
R~~CBIVE October D 3, 1933. Prasented before the Division of Colloid Chemistry at the 86th Meeting of the American Chemical Society, Chicago, Ill., September 10 to 15, 1933.
New Apparatus for Determination of Size Distribution of Particles in Fine Powders ROBERTT. KNAPP, California Institute of Technology, Pasadena, Calif.
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VERY year a greater need for accurate analysis of the size distribution of subsieve material is being
felt by the engineer, because of the increasingly vital part it plays in the manufacture of cement, pigments, and other powdered products. Sieves are a satisfactory means of obtaining this information as long as the material is relatively coarse, but when from 70 to 95 per cent of the sample passes the 200-mesh screen (the finest one giving consistent reading), some new scheme of analysis must be used. Several methods of analyzing this fine f r a c t i o n have been d e v e l o p e d . For example, P r o f e s s o r Work a t Columbia has perfected an excellent microscope technic. Elutriation and sedimentation methods employing various fluid m e d i a have been shown to be f e a s i b l e , and additional methods are constantly being developed, but FIGURE1. CUMULATIVE most of them are slow and DISTRIBUTION CURVE tedious. Some time ago the Riverside Cement Company inaugurated a comprehensive research program. A consideration of its:scope quickly showed that to carry on the program it was absolutely necessary to have some reliable method of making large numbers of subsieve analyses. After considerable study it was concluded that none of the existing instruments were satisfactory for the purpose; therefore, the development about to be described was undertaken. Before starting the design ,-loo of the instrument a careful 0’ analysis of the needs of the 3,a research program was made, t which resulted in setting up 8 the following five specifica5” ’D tions:
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1. High accuracy. 2. Ability t o d e t e r m i n e complete size distribution as & 0 T, distinguished from a fineness TIMe modulus or a value of total FIGURE 2. SETTLING CURVE surface. 3. Capacity for analyzing a lar e number of samples per day. Ability to use relatively large samples to reduce sampling errors. 5. Freedom from personal equation of the operator.
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The principle upon which the new instrument was to operate was then chosen by comparing the above specifica-
tions with the operating characteristics of existing instruments. The microscopic method was eliminated because it was too slow and employed too small a sample, Elutriators appeared unsuitable because of their doubtful accuracy and the length of time required to separate the sample into a large number of fractions. Methods involving light-scattering appeared to show promise for the determination of total surface but not for size distribution. In spite of the fact that existing instruments required prohibitive amounts of attention and their results were largely qualitative, the sedimentation method appeared to be the most promising; consequently this principle was adopted as the basis of the new design.
THEORY STOKES’ LAW. When a small body is allowed to fall freely in a viscous field, it soon reaches a velocity where the downward acceleration is balanced by the friction. Therefore, the velocity ceases to increase. This limiting velocity is expressed by the equation known as Stokes’ law
where V = velocity of fall g = acceleration of gravity u = density of falling substance urn = density of fluid medium q = viscosity of fluid medium r = radius of the particle
For the present purpose, the time required for a particle to fall a given distance is more interesting than the velocity. Therefore, the equation becomes
where T = time of fall H = height of fall
If the height, viscosity, and densities are held constant, this becomes (3)
K and K1 being constants. If a known weight of material composed of different sized particles is allowed to settle a distance H through a column of liquid, the relation between the weight of the material reaching the bottom and the time can be determined. By means of Equation 3, values of the radius, T, or diameter, d, can be substituted for the corresponding times, T,and the curve similar to Figure 1 constructed. This curve supplies the desired information about the size distribution of the particles in the sample. Unfortunately,
